She knew it. Or at least strongly suspected it. And that, she says, is the worst part.

Lynn Cisneros had always trusted her gut. It had never failed her.

And it didn’t that afternoon two Fridays ago. She just did not trust it.

“Who ever suspects abuse?” she said Tuesday in an interview. “Who ever thinks someone would intentionally do that to an infant?”

In fact, it turns out she was on the telephone to child protective services in California at the very moment her 7-month-old grandson, Cordero Izaiah Cisneros, was being beaten to death in El Cajon, Calif.

“I was on hold for over an hour,” she said. “I was at work and decided I would call Saturday, when I had all the time in the world.”

It was 3:19 p.m. March 18. She had just hung up the phone when she received a text message from Sharika Summers, the baby’s mother.

Cordero is very sick, the note said. He is having a terrible time breathing and is in the hospital.

She immediately sent an e-mail to her son, the baby’s father, Cordero Cisneros, 23, a culinary specialist in the Navy, who was on a ship somewhere in the Middle East.

Paramedics had found David Christopher Cruz, 21, walking aimlessly around an El Cajon apartment complex with the baby in his arms. The baby was not responsive.

At a San Diego hospital, the baby was put on life support. Cruz was arrested and held on $2 million bail.

Only weeks earlier, Lynn Cisneros, 57, had flown from her Englewood home to see her grandson. She loved little Cordero. Yes, she knew Sharika, also a sailor, had informed Lynn’s son via e-mail in January, a month after he deployed, that their relationship was over.

Sharika would not allow Lynn to stay in her son’s apartment, as she had always done. Lynn got a hotel room.

And then, there was little Cordero. He had bumps and bruises on his forehead and a bruise on his cheek.

Oh, he rolled off the bed, Sharika told her. Lynn Cisneros thought she had probably dropped him on the cement stairs and didn’t want to admit it. I tried to reach Sharika Summers but could not.

Something is wrong, Lynn Cisneros told herself.

The evening of March 18, she had just pulled into the parking lot at Park Meadows with her 22-year-old daughter, Sarina, when she received another text from Sharika.

“He is not going to live,” it read.

“I don’t know if I screamed, but people in the parking lot came rushing to help me,” she said.

She flew to San Diego the next morning. Her son, 23, was helicoptered off the USS Bunker Hill to a waiting airplane but would not arrive for another day.

“Can I touch him?” her son said as he stood over his broken infant. A nurse placed the brain-dead baby in the man’s arms.

“Mom,” he said, “this is not my son.”

Yes, it is, Lynn Cisneros replied, “only not the one you left in November.”

“He thought that when he got back,” she later said, “the baby would open his eyes and get better.”

The baby died a day later. Last week, Cruz, Sharika’s new boyfriend, pleaded not guilty to murder and child-abuse charges.

The cause of death has not been released. Doctors told Lynn Cisneros that every rib in the baby’s body had been broken.

“I blame myself in some ways,” she said. “I wish I had acted faster.”

That is why she called me. She asked if I would spread a message.

“Don’t be afraid,” she said, “and don’t automatically trust people. If you think something is wrong, there is a good chance it is. I just don’t want to see this happen to another totally helpless child.”

Cordero Cisneros will bring his son home to Englewood on Thursday. Services will be held Sunday.